In a steering apparatus for a vehicle, an intermediate shaft is provided, for instance, between a Cardan shaft joint provided on the side of a steering shaft and a Cardan shaft joint provided on the side of a steering gear.
The intermediate shaft is constructed of a male shaft and a female shaft that are so spline-fitted, etc. as not to be rotatable but to be slidable on each other. The intermediate shaft is structured to be capable of transferring a steering torque in a high rigidity state while preventing a backlash in order to surely transfer the steering torque given from a driver to the steering gear, absorbing an axis-directional displacement caused when the vehicle travels, and sliding (expandable/retractable) in the axial direction with a comparatively low and stable slide load so that the intermediate shaft can be expanded and retracted when disassembled and assembled.
The intermediate shaft has, for cutting uncomfortable “noises” and “vibrations” transferred to an interior of a car room from traveling wheels and from an engine room, a buffer mechanism provided between the intermediate shaft and a yoke of the Cardan shaft joint as disclosed in, e.g., German Patent Laid-Open Publication DE19905350A1.
In this buffer mechanism, a buffer member constructed by charging a space between an inner ring and an outer ring with a rubber, is provided between the intermediate shaft and the yoke of the Cardan shaft joint. When the steering torque is equal to or smaller than a predetermined level, the buffer member can buffer and reduce the uncomfortable noises and vibrations transferred from the engine room.
Note that the yoke is formed with a cut portion, while the intermediate shaft is provided with an engaging member (a protruded cam). Owing to this configuration, when the steering torque is equal to or smaller than the predetermined level, the engaging member does not engage with the cut portion, and when the steering torque rises to become equal to or larger than the predetermined level, the engaging member engages the cut portion, thus enabling the steering torque to be transferred. A feeling of sharp steering can be therefore acquired.
As described above, the intermediate shaft with the Cardan shaft joint has the buffer function in addition to the steering torque transfer function and the telescopic function.
It is, however, required that the buffer mechanism be provided on the side of the yoke of the Cardan shaft joint, and hence an effective utility space is reduced proportionally to a space for the buffer mechanism. This is a comparatively narrow portion, and nevertheless a scheme of effectively utilizing the space can not be attained. Further, this is a hindrance to decrease both the number of parts and manufacturing costs.
Moreover, a performance of absorbing the axis-directional displacement caused when the car travels and preventing the displacement and vibrations from being transferred onto a steering wheel, is required of the telescopic shaft of the steering mechanism of the car. Furthermore, the telescopic shaft is required to have a function by which a driver shifts and thus adjusts a position of the steering wheel in the axial direction in order to obtain an optimum position to driving the car.
In each of these cases, the telescopic shaft is required to reduce the backlash noises, an unpleasant feeling about the backlash on the steering wheel and a slide resistance during a slide operation in the axial direction.
Such being the case, the male shaft of the telescopic shaft has hitherto been coated with a film of nylon, and the slide portion has been greased, thereby absorbing or relieving metal noises, metal butting noises, etc. and reducing the slide resistance and the backlash caused in the rotating direction.
It might, however, happen that the film of nylon is increasingly abraded with an elapse of its use, with the result that the backlash in the rotating direction augments. Further, under a condition of being exposed to a high temperature within an engine room, the film of nylon changes in its volume and remarkably increases in slide resistance, and the abrasion thereof is conspicuously accelerated, resulting in an increase in the backlash in the rotating direction.
Under such circumstances, German Patent DE3730393C2 discloses that torque transfer members (spherical members) rolling when two shafts make relative movements in the axial direction, are fitted in between plural pairs of axially-extending grooves formed respectively in an outer peripheral surface of a male shaft and in an inner peripheral surface of a female shaft.
Further, according to German Patent DE3730393C2, a pre-load elastic body (leaf spring) for giving pre-load to the male shaft and the female shaft through a torque transfer member (spherical member), is provided between an inward or outward portion of the torque transfer member (spherical member) in a radial direction and each pair of axially-extending grooves.
With this configuration, when the torque is not transferred (when sliding), the leaf spring gives the pre-load to the torque transfer member (spherical member) against the female shaft to an extent large enough not to cause the backlash, thereby making it possible to prevent the backlash between the male shaft and the female shaft and enabling the male shaft and the female shaft to slide in the axial direction with a stable slide load without any backlash.
Moreover, when the torque is transferred, the leaf spring is capable of restricting the torque transfer member (spherical member) in a peripheral direction, and therefore the male shaft and the female shaft can transfer the torque in a high rigidity state while preventing the backlash in the rotating direction thereof.
Besides, according to structures disclosed in FIGS. 1 through 5 in German Patent DE3730393C2, one leaf spring for giving the pre-load to a set of torque transfer members (spherical members) is connected in the peripheral direction to another leaf spring for giving the pre-load to another set of torque transfer members (spherical members) adjacent thereto in the peripheral direction through a circular-arc connecting portion (web) extending in the peripheral direction.
The connecting portion (web) serves to generate the pre-load in the two leaf springs by applying tension or compression to the two leaf springs each other.
Note that according to structures disclosed in FIGS. 6 and 7 in German Patent DE3730393C2, the two leaf springs are not connected through the connecting member (web), however, a separate elastic body is interposed between the leaf spring and the axially-extending groove, thereby generating the pre-load in the radial direction.
In the structure disclosed in the above Patent Document, however, firstly, the pre-load is generated between the male shaft, the spherical member and the female shaft, and hence a curvature of the leaf spring and a curvature of the axially-extending groove has been changed so that the leaf spring may be disposed. The leaf spring is therefore unable to take a large quantity of flexure thereof. Note that a scatter in working accuracy, if any, is not allowable with the quantity of flexure to that extent.
Secondly, when the torque is inputted, the male shaft, the leaf spring, the spherical members and the female shaft get narrow down each other and thus transfer the torque, and therefore an extremely high surface pressure occurs at a contact point between the spherical member and the leaf spring. Namely, when the torque is transferred, a high stress occurs on the leaf spring, with the result that a “fatigue” of the leaf spring is induced by a permanent deformation, pre-load performance becomes hard to maintain over a long period of time, and this might be a hindrance to gain a longer life-time of the steering shaft.
Thirdly, when the torque is transferred, the leaf spring slides sideways in the peripheral direction from the axially-extending groove, whereby a decline of the transfer torque is induced, a degree of hysteresis can not be managed, and the hysteresis might excessively occur.
Fourthly, when a torque load is not applied, the contact points between the male shaft, the spherical member, the leaf spring and the female shaft do not exist on the same line, and hence contact angles change as the torque load is applied. As a result, neither a linear torsional characteristic necessary for the steering shaft nor the proper hysteresis might be obtained.
It is a first object of the present invention, which was devised under the circumstances described above, to provide a telescopic shaft for steering of a vehicle and a telescopic shaft for steering of a vehicle with a Cardan shaft joint that are capable of sliding with a stable slide load while surely preventing a backlash, transferring a torque in a high rigidity state and, besides, having two- or three-staged torsional rigidity characteristics while scheming to effectively utilize a space and to reduce the number of parts.